A track roller assembly and a reduction gear apparatus of a construction machine are equipped with ferrous floating seal parts for the purpose of preventing leakage of lubrication oil from inside thereof as well as entering of earth and sand therein. Accordingly, such floating seals are widely produced by applying adequate treatment in such that a seal sliding surface thereof is quenched to have a hard martensite structure, or a large amount of hard cementite and Cr7C3 carbide are crystallized in 30% by volume while transforming a parent phase to a martensite structure by quenching in order to improve seizure resistance and abrasion resistance. An exemplary floating seal is made by using a high-carbon and high-Cr cast iron or a Ni-hard cast iron (for example, as shown in Japanese Patent Publication (KOKAI) No. S51-59007).
In addition, a ferrous floating seal in which abrasion-resistant material is thermal-sprayed to a seal sliding surface thereof may be used for some purposes.
In the ferrous floating seal used for the purpose of sealing a lubrication oil in the reduction gears and the track rollers, a seal sliding surface thereof is abraded as fine particles of earth and sand are entered in the seal sliding surface by hulling motion in the earth and sand, and is lubed with the lubrication oil sealed therein. Accordingly, a ferrous floating seal capable of withstanding a very severe lubrication condition is required. Even if a most conventionally used hard ferrous floating seal part made of a high-carbon and high-Cr cast iron is applied, when setting pressure (press force) at assembling is high, considerable quenching crack (heat crack), seizure and abnormal abrasion occur on the seal sliding surface, resulting in leakage of oil.
And, even if various tool steels such as a cold work tool steel and a high speed steel (SKH material) are employed to increase the seizure resistance and the abrasion resistance, seizing due to defect of seizure resistance easily occurs, resulting in insufficient heat crack resistance and abrasion resistance. In addition, since such steels are very expensive, they have a problem that cost of material increases in view of material yield before a product is finished.
And, in resent years, construction machines such as a bulldozer are required to drive at a high speed for improvement in working efficiency, and therefore, the ferrous floating seal necessarily rotates at a high speed. This also causes quenching crack, seizure and abnormal abrasion, resulting in leakage of oil.
In order to solve the above-mentioned problems, an object of the present invention is to provide ferrous seal sliding parts excellent in heat crack resistance, seizure resistance and abrasion resistance and a producing method thereof.